The most common catalysts used in industry to manufacture styrene by dehydrogenation of ethylbenzene are based on iron (Fe), potassium (K) and cerium (Ce). The preparation of these catalysts consists of reacting a basic potassium salt, such as potassium carbonate, with an organic iron salt, EDTA for example. A possible active phase for the catalysis of dehydrogenation of ethylbenzene may be K.sub.2 FeO.sub.5. It has been discovered that cerium oxide has an effect on the improvement of the yield and the selectivity of the Fe/K based catalytic system. In the so called bulk catalyst, the amount of cerium is generally about 5 to about 10 weight percent. See U.S. Pat. No. 5,171,914, Shell Oil Co., issued Aug. 30, 1991; U.S. Pat. No. 5,023,225, United Catalysts Inc., issued Jul. 21, 1989; and German Patent DE 3,506,022, BASF A.G., issued Feb. 21, 1985.
The source of cerium used to make the catalyst can be cerium carbonate which is mixed together with the slurry of iron and potassium salts. Then, the slurry is calcined at high temperature, up to about 800.degree. C. This temperature is required to prepare the active iron/potassium phase and to obtain cerium oxide (CeO.sub.2). Like any catalyst, high surface area and thermal stability are needed in order to obtain higher activity. However, calcination of salts does not lead necessarily to high surface area materials.
In addition, it was discovered more recently that a higher cerium content compared to bulk catalysts can improve the selectivity and yield of the reaction. See German Patent DE 3,521,766, BASF A.G., issued Jun. 19, 1985 and U.S. Pat. No. 4,758,543, Dow Chem. Co., issued Jul. 19, 1988. As a conclusion of these studies, cerium oxide could be used as support for the Fe/K active phase. io However, the standard cerium oxide material has shown a very poor thermal stability at high temperature, particularly at temperatures higher than 800.degree. C.
Some additional compounds based on cerium have also been utilized. For example, cerium phosphate and Ce--Zr phosphates were found to be good catalysts for oxydehydrogenation of alkylaromatics and alkylpyridines. See U.S. Pat. No. 3,733,327, Dow Chemical Co., issued Jun. 28, 1971.
Moreover, the oxygen storage capacity (OSC) of ceria has been suspected to be responsible for the activity of cerium oxide. Thus, higher OSC materials can be taken into account for styrene catalysis. One of the effects of ceria is the decocking of the catalyst that may be poisoned after a period of time under reducing conditions.
The object of the present invention is to use stabilized Ce/Zr mixed oxide phases or solid solutions as active supports of a Fe/K based catalyst for the manufacture of styrene by dehydrogenation of ethylbenzene. The (Ce,Zr)O.sub.2 mixed oxides and preferably solid solutions present a very high thermal stability at high temperature as opposed to pure CeO.sub.2. They also show an improved OSC compared to ceria. These materials can be obtained by co-precipitation and co-thermohydrolysis.